(1) Field of the Invention
The present invention relates to arrays towed through the water by vessels and more particularly to an improved tow cable for the arrays in which the temperature at various radii of the tow cable is measurable thereby self-calibrating the tow cable to account for the heat-dissipation of the tow cable in order to measure the temperature of the water surrounding the tow cable.
(2) Description of the Prior Art
In naval operations, an array is towed behind a vessel for gathering information, such as the location of enemy vessels or the depth of the ocean. A typical array comprises an exterior hose wall fabricated from rugged, insulated material, and a plurality of information gathering wires communicating with acoustical sensors disposed within the protective hose wall. The conducting wires or optical fibers of the towed array transmit information via the tow cable to a microprocessor within the vessel for a readout of gathered data.
In addition to transmitting information, the tow cable also powers the array. Since the conducted power generates heat, the conducted power impacts the temperature of the cable and the water surrounding the cable. Further measurements that rely on the surrounding water temperature such as a sound velocity profile, can therefore be impacted by temperature variances along the length of the tow cable. Since no segment of the tow cable or only a minimal portion of the tow cable can be accessed on surface vessels, an accurate temperature measurement at different points along the length of the tow cable is difficult to discern after the tow cable is deployed or “let out” from the winch of the array handling system.
In the art, various methods and devices are employed to measure the temperature of the tow cable and the surrounding water column. In Seaman et al. (U.S. Pat. No. 6,147,931), an apparatus for providing a temperature profile of a towed sonar array is disclosed. In the cited reference, the tow cable for the array comprises a central cable and a protective outer jacket. Thermistors are disposed at spaced positions along the outer jacket and connect to conductors embedded in the outer jacket. The conductors terminate onboard ship to provide continuous signals representing temperatures at various ocean depths.
While thermistors can be positioned along the length of the tow cable to determine the temperature of the water, this use of thermistors is limited in its practical application. In a first example, using a high number of thermistors is impractical for a tow cable that can be as long as 8000 feet. Since each thermistor requires its own pair of conductors, the high number of thermistors can significantly increase the tow cable diameter over the length of the tow cable. In a second example, the technology of the cited reference is not easily transferable to the tow cable because of the strain encountered by the tow cable at the curvature of the cable to the winch of the towed array handling system. A separate protective band for the thermistor, as disclosed by the cited reference, is susceptible to detachment during repeated use of the tow cable such that the thermistor is easily exposed to these strains with the result of inaccurate information gathering if the thermistors are damaged.
In Yamaguchi et al. (U.S. Pat. No. 5,198,662), a measuring system measures temperature distribution in water using an optical fiber. In the cited reference, the optical fiber is positioned in a central pipe sealed by filler material. Although, the optical fiber positioned in this manner can determine the temperature of the proximate water column, the positioning of optical fibers as temperature sensors can be improved.
An improvement to the positioning of sensors for measuring temperature would be the ability to gather measurements at varying radii of the cable rather than only at the center of the cable. Gathering measurements at varying radii along a common vector from the center of the tow cable increases the accuracy of temperature measurements of the surrounding water column.